Posterior (acoustic) enhancement: anechoic structures (cysts) show brighter signals from areas beyond them in relation to the beam

Eggshell calcification: nodules surrounded by a layer of calcium have bright anterior and posterior walls due to a reflection from the surface, but posteriorly there is acoustic shadowing; this phenomenon also leads to edge artifact in which parallel dark lines extend posteriorly from the sides of nodules

Reverberation artifact: sound waves reflect off a very reflective surface and are re-reflected from the skin, resulting in phantom images behind the target image

Comet tail artifact: reverberation artifact from front and back of a very strong reflector / absorber (air bubble, metal fragment) - can also happen with dense colloid

Bayonet sign:

Due to speed propagation artifact - machines use average speed of sound to calculate depth

If sound actually travels faster in the tissue (anechoic or hypoechoic structures), a reflector will appear closer to the transducer than its actual depth and vice versa

A needle with its tip in a cyst or nodule with differing echogenicity from surrounding tissue will appear to have its tip bent due to this artifact, looking like a bayonet

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